Flashlamp



May 5, 195 3 J; A. M. VAN LIEMPT 2,637,185

FLASHLAMP Filed July 30, 1948 /N Vlf' N TOR Ja romes Alibi/21a Mar/a MinHemp?- av X ATTORNEY Patented May 5, 1953 FLASHLAMP Johannes AntoniusMaria Van Liempt, Eindhoven,Netherlands, assignor'to Corporacion cleVentas de Salitre y Yodo de Chile, Valparaiso, Chile, a company of ChileApplication July so, 1948, Serial No. 41,707

This invention relates to flash lamps, particularly for photographicpurposes, consisting of a bulb containing materials which on ignition byelectrical means emit strong actinic radiation; common materials are ametal, or metal alloy, usually aluminium or an alloy of aluminium andmagnesium, with a filling of oxygen or an oxygen "3 Claims. (Cl. 67-31)compound, or a mixture of gases which will support combustion, atsubstantially less than atmospheric pressure.

There is known to be a risk of the bulb of such a flash lamp beingshattered upon the lamp being ignited, and many safeguards have beenproposed to diminish the danger; the reduced pressure of. the filling isthe first of them. But it may happen that a leak develops in the lampwith the result that it fills with air to atmospheric pressure and isquite likely to be shattered when this air is heated by the combustionof the metal.

Attempts have been made to reduce the danger from such shattering byusing a double-walled bulb, or by enveloping the bulb in varnish-coatedgauze, or by making the bulb itself of laminated or other plastic. Otherattempts have been made to prevent explosion by making the occurrence ofleakage apparent to the user, for example by the provision of amanometer, or by causing the bulb to change colour on air entering it,for instance by the inclusion of nitric oxide in the filling or byputting in the bulb a complex cobalt compound which changes colour uponreaction with water vapour. Yet other attempts have been made to preventignition when it might prove dangerous, for instance by using amanometer to interrupt the electrical ignition circuit.

A principal object of the present invention is a flash lamp with apartly evacuated bulb the charge of which is rendered substantiallynoninflammable if leakage occurs.

A further object of the invention is a flash lamp containing-besides acombustible metal, a gas which will support combustion and a means ofignition=an additional reagent which upon leakage occurring combineswith the metal and the gas or one of them and thereby renders subsequentvigorous combustion impossible.

A more specific object of the invention is a flash lamp containing a drycombustible metal, a dry gas at less than atmospheric pressure whichwill support combustion of the metal, a means of ignition, and anadditional reagent which on moisture entering the lamp will combine withthe metal or the gas and thereby prevent their subsequent vigorouscombustion. Such a lamp depends for its protection on the fact that someordinarily vigorous chemical reactions do not take place in the totalabsence of moisture. Air entering by leakage brings with it enough waterto set the reaction in train, a very small amount sufficing since thewater appears to act catalytically. While such a reaction may bedesigned to consume in mild fashion the oxygen in the bulb as well asany that enters by leakage, for instance by the oxidation of phosphorusor of finely divided iron, it is preferable to provide for thecombustible metal itself to be attacked.

Accordingly, a further specific object of the invention is a flash lampcontaining a dry combustible metal which is not acted on by dry iodine,a dry gas at less than atmospheric pressure which will supportcombustion of the metal, and a charge of iodine suflicient in thepresence of moisture to corrode the Whole surface of the metal andthereby prevent subsequent vigorous combustion of the metal. It is notnecessary wholly to consume the metal; it is enough if it becomes coatedwith a reaction product which will sufficiently hinderaccess of oxygento the metal when a user attempts to ignite the bulb.

To this end a small amount of iodine is included in the bulb, or a smallamount of an iodine compound from which iodine is set free in thepresence of moisture. The bulb is made dry, and the metal whose surfaceis exposed in the bulb is one upon which iodine will not act in theabsence of moisture. Magnesium is liable to be attacked by dry iodineunder these conditions, and therefore magnesium, or alloys of aluminiumwith magnesium or other alkali or alkaline earth metals, should not beused unless they can be wholly encased in metal which is not attacked bydry iodine. Suitable metals unattacked by dry iodine are aluminium andalloys of aluminium with non-alkaline metals. Such alloys are alreadywell known and in common use in flash lamps and their precisecomposition forms no part of this invention. Bromine is a less effectivesubstitute for iodine, and has the disadvantage of being liquid.

As an example of the preferred method of carrying out the invention, aflash lamp bulb having aluminium foil or wire as the illuminant, may befilled with dry oxygen to a pressure of 400 mm. Hg, and a littlere-sublimed iodine may be included in the bulb, for instance by placinga small rod of compressed iodine powder in the exhaustion tube of thelamp. On admission of moisture the aluminium is attacked and soonbecomes coated with yellowish brown aluminium iodide, or with drops of asolution of that iodide. In course of time, if there is enough iodine,the whole of the aluminium will be converted into iodide. But that Inthe exhaustion tube 4 of the bulb there is placed a small rod 5 ofcompressed iodine powder.

The bulb is then evacuated through the-tubet in well known manner, andthe withdrawnis, replaced by a filling of dry oxygen at a pressure of400 mm. Hg. The filament leads are then connected to the terminals ofthe usual cap'G and the cap is cemented to the bulb.

The bulbs of flash lamps to which the invention is to be applied in thismanner should not be coated on their inner surface with plastic; forsafety purposes such a coating isnot necessary; if the coating is avehicle for colouring matter there is a possibility of reaction. withiodine changing the colour, and therefore coatings for coloured lampsshould be on the out.- side ofthe bulb.

I" claim:

1. A flash lamp comprising a transparent bulb containing aluminium foil,dry oxygen at less In close proximity to the filaa 4 than atmosphericpressure, suflicient iodine to corrode the Whole surface of thealuminium on access of moisture to the bulb, and an electric circuit forigniting the aluminium by the passage of current.

2. A flash lamp comprising a transparent bulb containing a metal,body=oi extendedform composedlat least chiefly of aluminium, dry, oxygenat less than atmospheric pressure, sufficient iodine to corrode thewhole surface of the metal body on access of moisture to the bulb, andan electric circuit for igniting the metal body by the passage of acurrent;

3. Afiashlampcomprising a transparent bulb containing axmetalbody ofextended form the surface of which consists chiefly of aluminium, dryoxygenat less than atmospheric pressure, sufiicient iodine to corrodethe whole surface of the: metal body on access of moisture to the bulb,and an electric circuit for igniting the metal body, by the passage ofcurrent.

JOHANNESAN'IONIUS MARIA VAN-LIEMPT.

References Cited in the, fileof thispatenti UNITED STATES. PATENTSNumber Name Date- Re. 18,678 Ostermeier Dec; 6,1932 989,572Van-Liemptetal. Jan; 29, 1935'

1. A FLASH LAMP COMPRISING A TRANSPARENT BULB CONTAINING ALUMINIUM FOIL,DRY OXYGEN AT LESS THAN ATMOSPHERIC PRESSURE, SUFFICIENT IODINE TOCORRODE THE WHOLE SURFACE OF THE ALUMINIUM ON